A range extender in a hybrid electric vehicle consists of a small internal combustion engine which drives an alternator to produce electrical energy. This electrical energy supplements the electrical energy stored in a battery or other electric energy storage device, which is used primarily to power the electric motor which propels the vehicle. Range extenders are used to extend the limited range of purely electric vehicles. Because current battery technology cannot provide the required electrical energy to give a pure electric vehicle sufficient range, an electric vehicle having a range extender offers a compromise between an internal combustion powered vehicle and a pure electric vehicle. An EV with a range extender is different than a HEV because the range extender engine is an auxiliary system, primarily used if the battery SOC is too low to complete the trip. This compromise improves vehicle performance and extends the vehicle's range while keeping emissions minimal.
The range extender engine may be selectively started if the state of the charge (SOC) of the battery is lower than required to meet driver torque demand, or if the battery SOC is not sufficient for the vehicle to reach a desired destination. If the range extender engine is started at ambient temperatures that are lower than the optimum operating temperature for engine and emissions components, such as fuel injectors, combustion chambers, oxygen sensors, catalytic converters, etc., engine performance may be degraded. For example, the range extender engine may display lower than optimum fuel efficiency, or increased engine wear, when starting due to the need to idle and warm up before the driver demanded torque can be delivered.
One way to increase fuel efficiency and reduce emissions is to preheat the range extender engine and/or other temperature sensitive engine components prior to engine start. Various types of preheaters may be employed for this task, such as coolant-based heaters, electric resistive heaters, heat pumps, heat pipes, etc. However, a common challenge encountered by each of these heating systems is determining when to initiate the preheating. If preheating is initiated too late, insufficient preheating will occur, resulting in decreased engine efficiency and increased tailpipe emissions at start-up. Alternatively, if preheating is initiated too early, greater than necessary amounts of energy will be expended by the preheating system to maintain the preheat temperature for an extended period of time. This is energetically inefficient, potentially costly, and may result in overheating of vehicle components.
Various approaches have been developed to accurately determine the required duration of vehicle component preheating to avoid issues associated with initiating preheating too early, or too late, as discussed above. One such approach, described by Matava et al. in U.S. Pat. No. 5,280,158, teaches a method for controlling the initiation and duration of preheating of vehicle engine/components. The method determines the required duration of preheater operation and initiates the preheating based on a manually selected time of next vehicle use, such that preheating is concluded at, or near, the time when the vehicle will next be started. The preheating is achieved via one or more electric resistive heaters, such as an engine block contact heater, a coolant heater, an engine oil heater, and a battery heater.
The inventors herein have recognized potential issues with the above approach. As one example, the method assumes that the temperature of the engine, or other vehicle components to be preheated, is initially at ambient temperature. However, based on the duration of operation of the motor, battery, inverter, and other electric components of the electric vehicle, the temperature of the range extender engine and other components may deviate from the ambient temperature (for example, they may be higher than the ambient temperature). The temperature may also be affected by the frequency of operation of the range extender engine on a given drive cycle. As another example, the method of Matava assumes that heat is transferred to vehicle components by the preheater at a constant rate or by a fixed amount. The heat transfer is not measured, but is inferred based on data provided by the manufacturer of said preheater. However, there may be preheaters which are unable to provide a constant output of heat. For example, in a coolant based system, the amount of heat that can be transferred to the engine by the coolant may depend on how many heat sources the coolant is coupled to, and how hot each heat source is. Even with heaters that provide a relatively constant heat output, such as electric resistive heaters, the heat output may change as the heater ages, if the heater degrades, or based on the power source coupled to the heater. If the preheating time is not correctly accounted for, there may be insufficient heating which can degrade the engine's performance, or there may be overheating which can degrade fuel economy and affect component life. As yet another example, the method of Matava requires the user to manually input a vehicle operation schedule so that the preheating time can be accordingly adjusted. However, there may be situations where the operator is unable to provide the input manually, such as when there is an unplanned change in vehicle destination, unexpected traffic delays, etc. Requiring frequent operator input to preheat the engine may also degrade the operator's drive experience.
In one example, the above issues may be addressed by a method for an electric vehicle comprising: transferring, via a heat exchange mechanism, waste heat from a vehicle drive motor and associated power electronics to pre-heat an internal combustion engine. In this way, an engine preheating may be more accurately coordinated with engine operation.
As an example, a vehicle may be configured with an electric motor for propelling vehicle wheels. The vehicle may further include a range extender engine that is intermittently operated when the state of charge of a battery driving the motor falls below a threshold. The engine is operated to charge the battery, or directly provide electrical energy to the motor, while the motor continues to propel the vehicle. Based on vehicle operating conditions such as a duration/distance of vehicle operation remaining until a destination is reached, an expected average power consumption along a planned route, a current battery state of charge (SOC) and an expected rate of drop in battery SOC, as well as driver aggressiveness, a vehicle controller may predict when the engine may be started. Based on ambient conditions, such as ambient temperature, wind charging, precipitation, etc., as well as a duration elapsed since a last time the engine was operated, the controller may infer an amount of preheating required for the engine, before the engine start. The controller may also calculate an amount of waste heat available on board the vehicle, such as based on measured or inferred temperature of one or more of the plurality of waste heat sources, as well as based on the amount of heat generated at one or more vehicle locations based upon vehicle operating conditions. The controller may schedule heat transfer from the waste heat sources to the engine upon comparing the amount of heat required for preheating the engine with the amount of waste heat available. For example, the scheduling may include transferring waste heat from an electric motor to a catalytic converter, based upon a measured or inferred temperature of the electric motor being greater than a threshold, and further based upon the temperature of the catalytic converter being below a threshold. In another example, the scheduling may including initiating said preheating such that the preheating is completed at or before the predicted engine start time. In another example, the scheduling may include ending preheating based upon an indication that the one or more range extender engine components being preheated has reached or surpassed a threshold temperature. Heat may be transferred via a heat exchange system including a plurality of heat exchangers thermally connected via a common fluid, such as coolant, which flows throughout the system, thereby transferring waste heat to one or more components of the range extender engine. Selection of which waste heat sources are utilized for preheating, which waste heat source is utilized to preheat which range extender engine component, and the extent/rate to which heat is transferred from said waste heat sources, may be based upon the temperatures of the waste heat sources, their spatial position relative to the range extender engine components, and the amount of preheating required by the range extender engine components. In one example, waste heat from an inverter may utilized to preheat one or more combustion chambers of a range extender engine based on the temperature of the inverter being greater than the temperature of the one or more combustion chambers, and further based on the inverter being located near the range extender engine. In another example, the rate of heat transfer out of the inverter, and into the combustion chambers, may be increased based upon an indication that the combustion chambers require a greater than a threshold amount of preheating.
In this way, by evaluating both the available waste heat, and the heat required for range extender engine preheating, a duration of preheating can be estimated. This estimated duration of preheating, in conjunction with a predicted engine start time, enables a controller of the vehicle to initiate preheating such that preheating is completed before or at the predicted engine start. As a result, under-heating or overheating of the engine is avoided. The technical effect of initiating heat transfer from waste heat sources in a vehicle propelled via electric motor, to a range extender engine, based on a predicted range extender engine start, is that preheating is completed within a threshold time of the predicted start. In this way, a more accurate and reliable preheating schedule can be provided, reducing the losses associated with over heating or under heating the engine. By preheating the engine, engine performance is improved, and the range of the electric vehicle is extended.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.